Plasma arc cutting is a metal working technique in which the heat required to sever, cut, or otherwise perform similar tasks on metals is provided by a plasma; i.e. a state in which matter has been heated to an extent and under other appropriate conditions for all of the elements to be present in ionized or atomic form. In most circumstances, the most efficient way to initiate and generate a plasma is to apply a sufficient potential difference (voltage drop) between an anode and a cathode in the presence of the plasma-forming material, typically a flowing gas. In one form of plasma arc welding known as transferred arc, the potential difference is applied between an electrode in the torch and a metal workpiece itself.
A plasma arc torch cutting system has a number of different applications, one of which is cutting. Cutting is sometimes initiated at the edge of a workpiece, but under other circumstances is started at some portion of the workpiece sufficiently displaced from an edge so that the edge does not come into account during the initial cutting. When a plasma arc torch is used to initiate an opening or a cut at such a position other than the edge, the technique is referred to as "piercing". Piercing raises a particular problem with plasma arc torches in that because of the location at which it takes place, there exists no edge or bottom opening (at least initially) into which molten metal can travel. Thus, in one typical side effect of piercing, molten metal in the cut tends to splash up against and damage the torch and its nozzle.
As known to those familiar with plasma arc welding and cutting torches, quite often the effect of damage to the nozzle will be reflected in damage to the electrode, and occasionally catastrophic damage to the entire plasma arc torch. Therefore, to the extent that the splash-back from piercing or other operations can be minimized or eliminated, the expected lifetime of the plasma arc torch can be extended.